Liquid crystal display device with spacers facing capacitive element

ABSTRACT

A liquid crystal display device comprises a pair of substrates which are arranged to face each other in an opposed manner while sandwiching liquid crystal therebetween, pixel regions which are formed on a liquid-crystal-side surface of one substrate out of the pair of substrates, and thin film transistors which are formed on respective pixel regions, wherein each thin film transistor includes a gate electrode connected to a gate signal line, a semiconductor layer laminated to the gate electrode by way of an insulation film, a drain electrode formed on the semiconductor layer and connected to a drain signal line, and a source electrode connected to a pixel electrode, and the semiconductor layer is formed in a periodically irregular shape in a zone having a width substantially larger than a width of the source electrode on a side thereof from which at least the source electrode is pulled out.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, andmore particularly to an active-matrix type liquid crystal displaydevice.

2. Description of the Related Art

In an active-matrix type liquid crystal display device, gate signallines which are extended in the x direction and are arranged in parallelin the y direction and drain signal lines which are extended in the ydirection and are arranged in parallel in the x direction are formed ona liquid-crystal-side surface of one substrate out of respectivesubstrates which are arranged to face each other in an opposed mannerwhile sandwiching liquid crystal therebetween.

Respective regions which are surrounded by these respective signal linesconstitute pixel regions and each pixel region is provided with a thinfilm transistor which is driven by a scanning signal supplied from thegate signal line and a pixel electrode to which a video signal issupplied from the drain signal line through the thin film transistor.

The pixel electrode generates an electric field between the pixelelectrode and a counter electrode which is arranged in an opposed mannerby way of the liquid crystal and liquid crystal is driven by thiselectric field such that the light transmittance thereof is changed.

Further, the pixel region is usually provided with a capacitive elementbetween the pixel electrode and the signal line having a stablepotential for storing the video signal supplied to the pixel electrodefor a relatively long time.

SUMMARY OF INVENTION

However, along with the recent demand for high definition, the liquidcrystal display device having such a constitution is largely affected bya drawback caused by the misalignment of the thin film transistor or thecapacitive element.

That is, when the misalignment of the thin film transistor or thecapacitive element is generated, the capacitance of the capacitiveelement is delicately changed and this generates the irregularities ofdisplay.

The present invention has been made in view of such a circumstance. Oneof the advantages of the present invention is enable a liquid crystaldisplay device to overcome the drawback caused by the misalignment ofthin film transistors or capacitive elements.

To briefly explain the summary of typical inventions out of inventionsdisclosed in this specification, they are as follows.

(1) A liquid crystal display device according to the present inventioncomprises, for example, a pair of substrates which are arranged to faceeach other in an opposed manner while sandwiching liquid crystaltherebetween, pixel regions which are formed on a liquid-crystal-sidesurface of one substrate out of the pair of substrates, and thin filmtransistors which are formed on respective pixel regions, wherein

the thin film transistor includes a gate electrode connected to a gatesignal line, a semiconductor layer laminated to the gate electrode byway of an insulation film, a drain electrode formed on the semiconductorlayer and connected to a drain signal line, and a source electrodeconnected to a pixel electrode, and

the semiconductor layer is formed in a periodically irregular shape in azone having a width substantially larger than a width of the sourceelectrode on a side thereof from which at least the source electrode ispulled out.

(2) A liquid crystal display device according to the present inventioncomprises, for example, a pair of substrates which are arranged to faceeach other in an opposed manner while sandwiching liquid crystaltherebetween, pixels which are formed on a liquid-crystal-side surfaceof one substrate out of the pair of substrates, and thin filmtransistors which are formed on respective pixels, wherein

the thin film transistor includes a gate signal line, a semiconductorlayer laminated to one region of the gate signal line by way of aninsulation film, a drain electrode formed on the semiconductor layer andconnected to a drain signal line, and a source electrode connected to apixel electrode,

the semiconductor layer is formed in a periodically irregular shape in azone having a width substantially larger than a width of the sourceelectrode on a side thereof from which at least the source electrode ispulled out, and

the gate signal line has a side thereof from which the source electrodeis pulled out stuck out in the vicinity of a region where the thin filmtransistor is formed whereby a width of the gate signal line isbroadened.

(3) A liquid crystal display device according to the present inventionis, for example, characterized in that:

on a liquid-crystal-side surface of one substrate out of a pair ofsubstrates which face each other in an opposed manner while sandwichingliquid crystal therebetween, a plurality of gate signal lines which arearranged in parallel and a plurality of drain signal lines which arearranged in parallel while crossing the respective gate signal lines areformed,

each pixel region which is surrounded by the gate signal lines and thedrain signal lines is provided with a thin film transistor which isdriven by scanning signals supplied from the one-side gate signal line,a pixel electrode to which video signals are supplied from the one-sidedrain signal line through the thin film transistor, and a capacitiveelement which is formed between the pixel electrode and the other-sidegate signal line, and

the capacitive element includes a first insulation film which is formedby extending the gate insulation film of the thin film transistor on theother-side gate signal line, a conductive layer which is formed on theinsulation film, a second insulation film which is formed by extending aprotective film covering the thin film transistor onto the conductivelayer, and an extension portion of the pixel electrode which is formedon the second insulation film, wherein the extension portion is formedon the conductive layer via a through hole formed in the secondinsulation film.

(4) A liquid crystal display device according to the present inventionis, for example, characterized in that:

on a liquid-crystal-side surface of one substrate out of a pair ofsubstrates which face each other in an opposed manner while sandwichingliquid crystal therebetween, a plurality of gate signal lines which arearranged in parallel and a plurality of drain signal lines which arearranged in parallel while crossing the respective gate signal lines areformed,

each pixel region which is surrounded by the gate signal lines and thedrain signal lines is provided with a thin film transistor which isdriven by scanning signals supplied from the one-side gate signal line,a pixel electrode to which video signals are supplied from the one-sidedrain signal line through the thin film transistor, and a capacitiveelement which is formed between the pixel electrode and the other-sidegate signal line,

the capacitive element includes a first insulation film which is formedby extending the gate insulation film of the thin film transistor on theother-side gate signal line, a conductive layer which is formed on theinsulation film, a second insulation film which is formed by extending aprotective film covering the thin film transistor onto the conductivelayer, and an extension portion of the pixel electrode which is formedon the second insulation film, wherein the extension portion is formedon the conductive layer via a through hole formed in the secondinsulation film, and

the conductive layer is formed such that the conductive layer isextended in the width direction of the gate signal line and strides overthe gate signal line.

(5) A liquid crystal display device according to the present inventionis, for example, characterized in that:

on a liquid-crystal-side surface of one substrate out of a pair ofsubstrates which are arranged to face each other in an opposed mannerwhile sandwiching liquid crystal therebetween, a plurality of gatesignal lines which are arranged in parallel and a plurality of drainsignal lines which are arranged in parallel while crossing therespective gate signal lines are formed,

each pixel region which is surrounded by the gate signal lines and thedrain signal lines is provided with a thin film transistor which isdriven by scanning signals supplied from the one-side gate signal line,a pixel electrode to which video signals are supplied from the one-sidedrain signal line through the thin film transistor, and a capacitiveelement which is formed between the pixel electrode and the other-sidegate signal line,

the capacitive element includes a first insulation film which is formedby extending the gate insulation film of the thin film transistor on theother-side gate signal line, a conductive layer which is formed on theinsulation film, a second insulation film which is formed by extending aprotective film covering the thin film transistor onto the conductivelayer, and an extension portion of the pixel electrode which is formedon the second insulation film, wherein the extension portion is formedon the conductive layer via a through hole formed in the secondinsulation film, and

the liquid crystal display device includes columnar spacers which areformed on a liquid-crystal-side surface of the other substrate out ofthe pair of substrates and face the inside of regions where thecapacitive elements are formed in an opposed manner, wherein the spacersare formed while obviating regions where the through holes are formed.

(6) A liquid crystal display device according to the present inventioncomprises, for example, a pair of substrates which are arranged to faceeach other in an opposed manner while sandwiching liquid crystaltherebetween, pixel regions which are formed on a liquid-crystal-sidesurface of one substrate out of the pair of substrates, and thin filmtransistors which are formed on respective pixel regions, wherein

each thin film transistor includes, on a gate electrode, a gateinsulation film, a semiconductor layer which is formed on the gateinsulation film and has an approximately semicircular pattern having anarcuate portion at the other pixel region side which is arranged whilesandwiching the gate electrode between the semiconductor layer and theother pixel region side, a drain electrode which is formed on thesemiconductor layer in an arcuate shape along the arcuate portion of thesemiconductor layer, and a source electrode which has a circular shapepositioned at a center point of the drain electrode forming the arcuateshape and has an extension portion which is extended toward the pixelregion side while ensuring a width substantially equal to a diameter ofthe circular shape, and

the semiconductor layer is formed in a periodically irregular shape in azone having a width substantially larger than a width of the sourceelectrode on a side other than the arcuate portion from which the sourceelectrode is pulled out.

(7) A liquid crystal display device according to the present inventionis, for example, characterized in that:

on a liquid-crystal-side surface of one substrate out of a pair ofsubstrates which face each other in an opposed manner while sandwichingliquid crystal therebetween, a plurality of gate signal lines which arearranged in parallel and a plurality of drain signal lines which arearranged in parallel while crossing the respective gate signal lines areformed,

each pixel region which is surrounded by the gate signal lines and thedrain signal lines is provided with a thin film transistor which isdriven by scanning signals supplied from the one-side gate signal line,a pixel electrode to which video signals are supplied from the one-sidedrain signal line through

the thin film transistor, and a capacitive element which is formedbetween the pixel electrode and the other-side gate signal line, thethin film transistor includes, on the one-side gate signal line, a gateinsulation film, a semiconductor layer which is formed on the gateinsulation film and has an approximately semicircular pattern having anarcuate portion at the other pixel region side which is arranged whilesandwiching the one-side gate signal line between the semiconductorlayer and the other pixel region side, a drain electrode which is formedon the semiconductor layer in an arcuate shape along the arcuate portionof the semiconductor layer, and a source electrode which has a circularshape positioned at a center point of the drain electrode forming thearcuate shape and has an extension portion which is extended toward thepixel region side while ensuring a width substantially equal to adiameter of the circular shape, and

the capacitive element includes a first insulation film which is formedby extending the gate insulation film of the thin film transistor on theother-side gate signal line, a second insulation film which is formed byextending a protective film covering the thin film transistor, and anextension portion of the pixel electrode which is formed on the secondinsulation film, and

the other-side gate signal line which constitutes a portion of thecapacitive element is provided with a projection portion which issuperposed on a portion of the pixel electrode of other pixel regionwhich sandwiches the gate signal line with the pixel region.

(8) A liquid crystal display device according to the present inventioncomprises, for example, a pair of substrates which are arranged to faceeach other in an opposed manner while sandwiching liquid crystaltherebetween, pixel regions which are formed on a liquid-crystal-sidesurface of one substrate out of the pair of substrates, and thin filmtransistors which are formed on respective pixel regions, wherein

the thin film transistor includes, on a gate electrode, a gateinsulation film, a semiconductor layer which is formed on the gateinsulation film and has an approximately semicircular pattern having anarcuate portion at the other pixel region side which is arranged whilesandwiching the gate electrode between the semiconductor layer and theother pixel region side, a drain electrode which is formed on thesemiconductor layer in an arcuate shape along the arcuate portion of thesemiconductor layer, and a source electrode which has a circular shapepositioned at a center point of the drain electrode forming the arcuateshape and has an extension portion which is extended toward the pixelregion side while ensuring a width substantially equal to a diameter ofthe circular shape, and

the gate electrode includes a projection portion which is superposed onthe source electrode at a side thereof from which a source electrode ofthe thin film transistor is pulled out and is extended in the extendingdirection of the source electrode.

(9) A liquid crystal display device according to the present inventionis, for example, characterized in that:

on a liquid-crystal-side surface of one substrate out of a pair ofsubstrates which face each other in an opposed manner while sandwichingliquid crystal therebetween, a plurality of gate signal lines which arearranged in parallel and a plurality of drain signal lines which arearranged in parallel while crossing the respective gate signal lines areformed,

each pixel region which is surrounded by the gate signal lines and thedrain signal lines is provided with a thin film transistor which isdriven by scanning signals supplied from the one-side gate signal line,a pixel electrode to which video signals are supplied from the one-sidedrain signal line through the thin film transistor, and a capacitiveelement which is formed between the pixel electrode and the other-sidegate signal line,

the thin film transistor includes, on the one-side gate signal line, agate insulation film, a semiconductor layer which is formed on the gateinsulation film and has an approximately semicircular pattern having anarcuate portion at the other pixel region side which is arranged whilesandwiching the one-side gate signal line between the semiconductorlayer and the other pixel region side, a drain electrode which is formedon the semiconductor layer in an arcuate shape along the arcuate portionof the semiconductor layer, and a source electrode which has a circularshape positioned at a center point of the drain electrode forming thearcuate shape and has an extension portion which is extended toward thepixel region side while ensuring a width substantially equal to adiameter of the circular shape,

the capacitive element includes at least a first insulation film whichis formed by extending the gate insulation film of the thin filmtransistor on the other-side gate signal line, a second insulation filmwhich is formed by extending a protective film covering the thin filmtransistor, and an extension portion of the pixel electrode which isformed on the second insulation film,

the second insulation film is formed of either an organic material layeralone or a sequential laminated body made of an inorganic material layerand an organic material layer, and

the other-side gate signal line which constitutes a portion of thecapacitive element is provided with a projection portion which issuperposed on a portion of the pixel electrode of other pixel regionwhich sandwiches the gate signal line with the pixel region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing one embodiment of a pixel of a liquidcrystal display device according to the present invention.

FIG. 2 is an overall plan view showing one embodiment of the liquidcrystal display device according to the present invention.

FIG. 3 is across-sectional view taken along a line III—III of FIG. 1.

FIG. 4 is an explanatory view showing an advantageous effect of theliquid crystal display device according to the present invention.

FIG. 5 is a plan view of an essential part showing another embodiment ofthe liquid crystal display device according to the present invention.

FIG. 6 is a plan view showing another embodiment of the pixel of theliquid crystal display device according to the present invention.

FIG. 7 is a plan view showing another embodiment of the pixel of theliquid crystal display device according to the present invention.

FIG. 8 is a cross-sectional view taken along a line VIII—VIII of FIG. 7.

FIG. 9 is across-sectional view showing another embodiment of the pixelof the liquid crystal display device according to the present invention.

FIG. 10 is a plan view showing another embodiment of the pixel of theliquid crystal display device according to the present invention.

FIG. 11 is a cross-sectional view taken along a line XI—XI of FIG. 10.

FIG. 12 is a plan view showing another embodiment of the pixel of theliquid crystal display device according to the present invention.

FIG. 13 is a cross-sectional view taken along a line XIII—XIII of FIG.12.

FIG. 14 is a plan view of an essential part showing another embodimentof the liquid crystal display device according to the present invention.

FIG. 15 is a plan view showing another embodiment of the pixel of theliquid crystal display device according to the present invention.

FIG. 16 is a plan view of an essential part showing another embodimentof the pixel of the liquid crystal display device according to thepresent invention.

FIG. 17 is a plan view of an essential part showing another embodimentof the pixel of the liquid crystal display device according to thepresent invention.

FIG. 18 is a plan view showing another embodiment of the pixel of theliquid crystal display device according to the present invention.

FIG. 19 is a plan view showing another embodiment of the pixel of theliquid crystal display device according to the present invention.

FIG. 20 is a plan view of a portion of the pixel which is prepared byconsidering dimensions which are determined at an actual design stagebased on the constitution shown in FIG. 18.

DETAILED DESCRIPTION

Preferred embodiments of a liquid crystal display device according tothe present invention are explained hereinafter in conjunction withattached drawings.

EMBODIMENT 1

FIG. 2 is a plan view showing one embodiment of the liquid crystaldisplay device according to the present invention.

In the drawing, a pair of transparent substrates SUB1 and SUB2 which arearranged to face each other in an opposed manner by way of liquidcrystal. The liquid crystal is filled in a space defined by a pair ofthese transparent substrates SUB1, SUB2 using a seal member SL whichalso performs a function of fixing the other transparent substrates SUB2to one transparent substrate SUB1.

On a liquid-crystal-side surface of one transparent substrate SUB1 whichis surrounded by the seal member SL, gate signal lines GL which areextended in the x direction and are arranged in parallel in the ydirection and drain signal lines DL which are extended in the ydirection and are arranged in parallel in the x direction are formed.

Regions which are surrounded by respective gate signal lines GL andrespective drain signal lines DL constitute pixel regions and a mass ofthese pixel regions arranged in a matrix array constitutes a liquidcrystal display part AR.

Each pixel region is provided with a thin film transistor TFT which isdriven by a scanning signal supplied from the one-side gate signal lineGL and a pixel electrode PX to which a video signal is supplied from theone-side drain signal line DL through the thin film transistor TFT.

The pixel electrode PX generates an electric field between the pixelelectrode PX and a counter electrode (not shown in the drawing) which isformed in common with respective pixel regions at the other transparentsubstrate SUB2 side. The light transmittance of the liquid crystal iscontrolled in response to the electric field.

Respective one ends of the gate signal lines GL are extended over theseal member SL and the extended ends constitute terminals to whichoutput terminals of a vertical scanning driving circuit V are connected.Further, signals supplied from a printed circuit board which is arrangedoutside a liquid crystal display panel are inputted to input terminalsof the vertical scanning driving circuit V.

The vertical scanning driving circuit V is constituted of a plurality ofsemiconductor devices, wherein a plurality of neighboring gate signallines are formed into a group and one semiconductor device is allocatedto each group.

In the same manner, respective one ends of the drain signal lines DL areextended over the seal member SL and these extended ends constituteterminals to which output terminals of a video signal driving circuit Heare connected. Further, signals supplied from a printed circuit boardwhich is arranged outside the liquid crystal display panel are inputtedto input terminals of the video signal driving circuit He.

The video signal driving circuit He is also constituted of a pluralityof semiconductor devices, wherein a plurality of neighboring drainsignal lines DL are formed into a group and one semiconductor device isallocated to each group.

Respective gate signal lines GL are configured to be sequentiallyselected one after another in response to the scanning signals suppliedfrom the vertical scanning circuit V.

Further, the video signals are supplied to the respective drain signallines DL from the video signal driving circuit He at the timing whichmatches the selection of the gate signal lines GL.

FIG. 1 is a view showing the constitution of the pixel region and FIG. 3is a cross-sectional view taken along a line III—III of FIG. 1.

In FIG. 1, first of all, a pair of gate signal lines GL which areextended in the x direction and are arranged in parallel in theydirection are formed on the liquid-crystal-side surface of thetransparent substrate SUB1.

These gate signal lines GL surround a rectangular region together with apair of drain signal lines DL which will be explained later and thisregion constitutes the pixel region.

Here, light shielding films CL are formed simultaneously with theformation of these gate signal lines GL, wherein the light shieldingfilms CL are provided at left and right sides of the pixel region and inparallel to and close to the drain signal lines DL.

These light shielding films CL define the pixel region together with ablack matrix formed at the transparent substrate SUB2 side. Due to thepresence of the light shielding films CL, the tolerance at the time ofaligning the transparent substrate SUB2 to the transparent substrateSUB1 can be increased.

On a surface of the transparent substrate SUB1 on which the gate signallines GL and the light shielding films CL are formed in theabove-mentioned manner, an insulation film GI made of SiN, for example,is formed such that the insulation film GI also covers the gate signallines GL.

The insulation film GI performs a function of an interlayer insulationfilm with respect to the gate signal lines GL in a region in which thedrain signal lines DL are formed as will be explained later, performs afunction of a gate insulation film in a region in which the thin filmtransistor TFT is formed as will be explained later, and performs afunction of a dielectric film in a region in which a capacitive elementCadd is formed as will be explained later.

Then, on a surface of the insulation film GI, a semiconductor layer ASmade of amorphous Si, for example, is formed such that the semiconductorlayer AS is superposed on a portion of the gate signal line GL.

The semiconductor layer AS constitutes a part of the thin filmtransistor TFT. By forming a drain electrode SD1 and a source electrodeSD2 on an upper surface of the semiconductor layer AS, it is possible toform an MIS type transistor having an inverse staggered structure whichemploys a portion of the gate signal line GL as a gate electrode.

Here, the drain electrode SD1 and the source electrode SD2 aresimultaneously formed with the formation of the drain signal lines DL,for example.

That is, the drain signal lines DL which are extended in the y directionand are arranged in parallel in the x direction are formed, the portionsof the drain signal lines DL are extended over upper surfaces of thesemiconductor layers AS so as to form the drain electrodes SD1, and eachsource electrode SD2 is formed such that each source electrode SD2 isspaced apart from each drain electrode SD1 by a distance correspondingto a length of a channel of the thin film transistor TFT.

The source electrode SD2 is slightly extended over an upper surface ofthe insulation film GI at the pixel region side from the surface of thesemiconductor layer AS so as to form a contact portion CN which isserved for the connection between the source electrode SD2 and the pixelelectrode PX which will be explained later.

Here, the semiconductor layer AS is formed in a serrated pattern whichperiodically repeats projection and indentation at least at a sideportion from which the source electrode SD2 which is formed on an upperlayer of the semiconductor layer AS is pulled out to a region where thesemiconductor layer AS is not formed.

The reason that such a constitution is adopted is to overcome a drawbackcaused by the discontinuity of the source electrode SD2 at a steppedportion of the semiconductor layer AS. That is, by increasing the lengthof the stepped portion by adopting the above-mentioned serrated pattern,it is possible to prevent a portion where the discontinuity occurs fromcovering the whole stepped portion.

Further, in the formation of the source electrode SD2 on thesemiconductor layer AS, even when the misalignment (particularly, themisalignment in the x direction) of the source electrode SD2 isgenerated, it is possible to prevent the change of the area of thesource electrode SD which is superposed on the semiconductor layer AS.

Here, why the misalignment in the x direction is to be taken intoaccount is that, with respect to the liquid crystal display part AR, aside thereof in the x direction is generally larger than a side thereofin the y direction and hence, the misalignment in the x direction islarger than the misalignment in the y direction whereby the misalignmentin the x direction can not be ignored.

Here, thin layers doped with impurities of high concentration are formedon an interface between the semiconductor layer AS and the drainelectrode SD1 and an interface between the semiconductor layer AS andthe source electrode SD2 and these layers function as contact layers.

With respect to these contact layers, at the time of forming thesemiconductor layer AS, for example, an impurity layer of highconcentration is formed on a surface of the semiconductor layer ASpreliminarily and, using the drain electrode SD1 and the sourceelectrode SD2 formed on an upper surface of the semiconductor layer ASas masks, the impurity layer which is exposed from the drain electrodeSD1 and the source electrodes SD2 are etched to form the contact layers.

On the surface of the transparent substrate SUB1 on which the thin filmtransistors TFT, the drain signal lines DL, the drain electrodes SD1 andthe source electrodes SD2 are formed, a protective film PSV which isconstituted of a sequential laminated body formed of an inorganicmaterial layer made of SiN or the like and an organic material layersuch as resin, for example, is formed. The protective film PSV isprovided as a layer which obviates the direct contact between the thinfilm transistors TFT and the liquid crystal and can prevent thedeterioration of the characteristics of the thin film transistors TFT.

Pixel electrodes PX are formed on an upper surface of the protectivefilm PSV. Each pixel electrode PX is constituted of a light-transmittingconductive film formed of an ITO (Indium-Tin-Oxide) film, for example.

The pixel electrode PX is formed such that the pixel electrode PXoccupies the most portion of the pixel region while obviating a regionwhere a thin film transistor TFT is formed. The pixel electrode PX has aportion thereof electrically connected with the source electrode SD2 ofthe thin film transistor TFT via a contact hole CH formed in a portionof the protective film PSV.

Further, the pixel electrode PX is extended over other neighboring gatesignal line GL which is different from the gate signal line GL fordriving the thin film transistor TFT which is connected to the pixelelectrode PX thus forming a portion which is superposed on the othergate signal line GL.

In this portion, the capacitive element Cadd which uses theabove-mentioned protective film PSV as a dielectric film is formedbetween the pixel electrode PX and the other gate signal line GL.

The capacitive element Cadd is configured to have a function of storingthe video signal supplied to the pixel electrode PX for a relativelylong time, for example.

On the upper surface of the transparent substrate SUB1 on which thepixel electrodes PX are formed, an orientation film (not shown in thedrawing) is formed such that the orientation film also covers the pixelelectrodes PX. The orientation film is a film which is brought intodirect contact with the liquid crystal and determines the initialorientation direction of liquid crystal molecules by a rubbing formed ona surface thereof.

With respect to the liquid crystal display device having such aconstitution, as mentioned previously, at the time of forming the sourceelectrodes SD2 of the thin film transistors TFT, even when themisalignment (particularly, the misalignment in the x direction in thedrawing) is generated with respect to the semiconductor layer AS, thearea of the portion where the semiconductor layer AS and the sourceelectrode SD are superposed each other remains unchanged.

FIG. 4 is an explanatory view showing a case in which the sourceelectrode SD is normally formed with respect to the semiconductor layerAS and cases in which the source electrode SD is moved in the left andright directions with respect to the semiconductor layer AS.

Since the side of the semiconductor layer AS from which the sourceelectrode SD2 is pulled out is formed in a serrated pattern whichperiodically repeats projection and indentation, a followingrelationship can be established. That is, even when the source electrodeSD2 is displaced and increases the superposition with the semiconductorlayer AS at one side in the displacement direction, the source electrodeSD2 decreases the superposition with the semiconductor layer AS at theother side opposite to one side in the moving direction by an amountcorresponding to the increase of the superposition.

Accordingly, the gate-source capacitance (Cgs) of the thin filmtransistor TFT can be held at a fixed value and remains unchangedirrespective of the misalignment of the source electrode SD2.

As can be understood from the above-mentioned explanation, it isnecessary for the periodically irregular shape to be formed on thesemiconductor layer AS in a width span which has a width larger than awidth of the source electrode SD2 and such a width is determined basedon the maximum value of the misalignment of the source electrode SDwhich is obtained by experience.

In the above-mentioned embodiment, the repetition of periodicallyirregularities formed on the side of the semiconductor layer AS fromwhich the source electrode SD2 is pulled out defines a serrated shapewhich is formed by bending a straight line in a zigzag shape. However,the periodically irregular shape is not determined in a strict sense andmay adopt patterns shown in FIG. 5A to FIG. 5D. In short, theadvantageous effect of the present invention is achieved by a pattern byrepeating the periodically irregularities of same shape.

EMBODIMENT 2

FIG. 6 is a view showing the constitution of another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 1.

The constitution which renders this embodiment different from theembodiment shown in FIG. 1 is that, a gate signal line GL widens aportion thereof in the vicinity where a semiconductor layer AS of a thinfilm transistor TFT is superposed on the gate signal line. Particularly,a side portion of the gate signal line GL from which a source electrodeSD2 of the thin film transistor TFT is pulled out is formed in a patternwhich is projected or stuck out toward the pixel region side.

Due to such a constitution, it is possible to obviate the generation ofa phenomenon that the misalignment of the semiconductor layer AS withrespect to the gate signal line GL, makes a portion of the semiconductorlayer AS stuck out from the gate signal line GL.

Advantageous effect by the above-mentioned characteristic pattern of thesemiconductor layer AS shown in the embodiment 1 can be obtained on thepremise that the semiconductor layer AS is superposed on the gate signalline GL and cannot be obtained when the portion of the semiconductorlayer AS is stuck out from the gate signal line GL.

EMBODIMENT 3

FIG. 7 is a view showing the constitution of another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 1. Further, FIG. 8 is a cross-sectional view takenalong a line VIII—VIII of FIG. 7.

The constitution which renders this embodiment different from theembodiment shown in FIG. 1 lies in a capacitive element Cadd. That is, aconductive layer CND is formed on a substrate SUB1 by way of a gatesignal line GL and an insulation film GI, and the conductive layer CNDis connected to an extension portion of a pixel electrode PX via athrough hole formed in a protective film PSV formed as a layer above theconductive layer CND.

Here, the conductive layer CND is formed simultaneously with theformation of drain signal lines DL, for example.

Due to such a constitution, it is possible to increase the capacity ofthe capacitive element Cadd without decreasing an aperture portion of apixel region.

In this case, however, it is deniable that corresponding to the increaseof the capacitance of the capacitive element Cadd, the fluctuation ofthe capacitance value is increased due to the misalignment of theconductive layer CND by an amount corresponding to the increased amountof capacitance of the capacitive element Cadd.

To cope with such a drawback, in this embodiment, the conductive layerCND is formed such that the conductive layer CND sufficiently stridesover the gate signal line GL in the widthwise direction of the gatesignal line GL. Due to such a constitution, even when the misalignmentin the y direction in the drawing in the embodiment is generated withrespect to the conductive layer CND, the area of a portion where theconductive layer CND and the gate signal line GL are superposed eachother remains unchanged and hence, it is possible to obtain anadvantageous effect that the capacitance of the capacitive element Caddis not fluctuated.

As shown in FIG. 8, assuming a width of the gate signal line GL as W5, ahang-out width of one hang-out portion of the conductive layer CNDformed astride the gate signal line GL as W4 and a spaced-apart distancebetween the gate signal line GL and the pixel electrode PX as W3, bysetting these factors such that the relationship expressed by afollowing formula is established, the increase of parasitic capacitanceof the pixel electrode PX can be obviated and, at the same time, thefluctuation of capacitance value of the capacitive element Cadd can besuppressed.¼×W3≦W4≦¾×W3  (1)

Further, this embodiment is configured such that no countermeasure istaken to cope with the misalignment between the thin film transistor TFTand the source electrode SD2 thereof. However, it is needless to saythat the constitution described in Embodiment 1 and Embodiment 2 can beadopted as it is.

EMBODIMENT 4

FIG. 9 is a view showing the constitution of another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 8.

The constitution which renders this embodiment different from theembodiment shown in FIG. 8 is that a protective film PSV is formed of asequential laminated body consisting of a protective film IPAS made ofan inorganic material layer and a protective film OPAS made of anorganic material layer, and the electrical connection between theconductive layer CND and the pixel electrode PX is established via athrough hole formed in the sequential laminated body.

Due to the formation of such a protective film PSV, it is possible toflatten the surface of the protective film PSV and hence, the rubbingtreatment of an orientation film ORIL which is formed covering not onlythe protective film PSV but also the pixel electrodes PX can beperformed reliably. Further, although it is deniable that thecapacitance value of the capacitive element Cadd is reduced due to theformation of the protective film OPAS made of an organic material layer,this embodiment has an advantageous effect that a reduction amount ofthe capacitance value can be suppressed within a range of extremelysmall amount.

Although, in this embodiment, the protective film PSV is formed of thesequential laminated body consisting of the protective film IPAS made ofthe inorganic material layer and the protective film OPAS made of theorganic material layer, it is needless to say that a similaradvantageous effect can be obtained even when the protective film PSV isformed of only the protective film OPAS made of the organic materiallayer.

Further, this embodiment is not provided with a measure to cope with themisalignment between the thin film transistor TFT and the sourceelectrode SD2 thereof. However, it is needless to say that thisembodiment can also directly adopt the constitution described either inthe embodiment 1 or the embodiment 2.

EMBODIMENT 5

FIG. 10 is a view showing the constitution of another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 7. Further, FIG. 11 is a cross-sectional view takenalong a line XI—XI of FIG. 10.

The constitution which renders this embodiment different from theembodiment shown in FIG. 7 lies in that a pixel electrode PX is extendedto a gate signal line GL side such that the pixel electrode PX issuperposed on a portion of an x direction side of the gate signal lineGL. Further, the pixel electrode PX is also extended to drain signalline DL sides and is superposed on portions of the drain signal linesDL.

Due to such a constitution, the numerical aperture of a pixel region canbe enhanced. In this case, although the pixel electrode PX is partiallysuperposed on the conductive layer CND, the capacitance which isgenerated between the pixel electrode PX and the conductive layer CNDcan be largely suppressed due to a protective film OPAS made of organicmaterial whereby it is possible to obtain an advantageous effect that anadverse effect to an image quality can be prevented.

EMBODIMENT 6

FIG. 12 is a view showing the constitution of another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 7. Further, FIG. 13 is a cross-sectional view takenalong a line XIII—XIII of FIG. 12.

The constitution which renders this embodiment different from theembodiment shown in FIG. 13 lies in that the constitution of spacers SPwhich are provided for forming a gap between a transparent substrateSUB1 and a transparent substrate SUB2 uniform is explicitly defined.

That is, the spacers SP are constituted of columnar spacers SP which areformed on a liquid-crystal-side surface of the transparent substrateSUB2. These spacers SP are formed to face capacitive elements Cadd in anopposed manner. A region where the capacitive element Cadd is formed hasa relatively large area. Accordingly, by arranging the spacers SP toface the capacitive element Cadd, it is possible to prevent thereduction of the numerical aperture.

The columnar spacers SP are formed by selectively etching an organicmaterial layer applied to a whole liquid-crystal-side surface of thetransparent substrate SUB2 using a photolithography technique andpositions where these spacers SP are formed can be arbitrarilydetermined.

Then, the columnar spacer SP is arranged in the inside of the regionwhere the capacitive element Cadd is formed while obviating a throughhole portion CH which is provided for connecting a conductive layer CNDand a extention portion of a pixel electrode PX to each other. This isbecause that when the spacer SP is arranged to face the through holeportion CH in an opposed manner, the gap accuracy cannot be ensured.

Further, as shown in FIG. 13, assuming a size of a top portion of thespacer SP (a diameter when a cross-section of the spacer SP is circularand a width when the cross-section is rectangular) as W6 and a size of abottom surface of the through hole portion CH (a diameter when across-section of the through hole portion CH is circular and a widthwhen the circular cross-section is rectangular) as W7, it is desirableto determine the relationship between these sizes as W6>W7.

Such a provision is adopted to prevent a phenomenon that at the time ofaligning the transparent substrate SUB2 to the transparent substrateSUB1, the relative position between these substrates is delicatelydisplaced so that the spacer SP is completely fitted into the throughhole portion CH and cannot be pulled out from the through hole portionCH.

Here, so long as the spacer SP is formed in the inside of the regionwhere the capacitive element Cadd is formed and at the position whichcan obviate the through hole portion CH, the spacer SP may be arrangedat a position shown in FIG. 14A to FIG. 14C, for example.

EMBODIMENT 7

FIG. 15 is a view showing the constitution of another embodiment of aliquid crystal display device according to the present invention andcorresponds to FIG. 12.

The constitution which renders this embodiment different from theembodiment shown in FIG. 12 lies in the constitution of thin filmtransistors TFT. That is, in each thin film transistor TFT, asemiconductor layer AS is formed in an approximately semicircularpattern having an arcuate portion at a side opposite to a pixel region,a drain electrode SD1 is formed in an arcuate shape along the arcuateportion of the semiconductor layer AS, and a source electrode SD2 has acircular shape and is positioned at a center point of the arcuate drainelectrode SD1. The source electrode SD2 is formed such that the sourceelectrode SD2 has also an extension portion which has a width equal tothe diameter thereof and extended toward the pixel region side.

The thin film transistor TFT having such a constitution has a writingability which corresponds to a length of the arcuate drain electrode SD1and the width of the source electrode SD2 can be made considerably smalland hence, gate-source capacitance (Cgs) can be reduced and thefluctuation of the capacitance can be also reduced.

However, when the width of the source electrode SD2 is small, a brokenstep is liable to occur at a stepped portion of the semiconductor layerAS. This embodiment is characterized in that, particularly with respectto the semiconductor layer AS formed in an approximately semicircularpattern, a portion excluding the arcuate portion, that is, a sideportion from which the source electrode SD2 is pulled out is formed in aperiodically irregular shape.

Due to such a constitution, the stepped portion of the semiconductorlayer AS which is coated with the source electrode SD2 can increase thelength thereof by the zigzag arrangement so that even when the brokenstep occurs at one portion, it is possible to ensure the electricalconnection at other portions.

Further, in the same manner as the embodiment 1, this embodiment alsocan enjoy an advantageous effect that even when the displacement ariseswith respect to the alignment of the source electrode SD2 to thesemiconductor layer AS, the fluctuation of the gate-source capacitance(Cgs) is hardly generated.

Although the drain electrode SD1 is formed in a semicircular shape inthis embodiment, the shape of the drain electrode SD1 is not limited tosuch a shape. For example, it is needless to say that, as shown in FIG.16, the drain electrode SD1 may be formed in an arcuate shape having anopening angle of approximately 60°. This is because the opening angle ofdrain electrode SD1 is determined depending on the setting of a channelwidth of the thin film transistor TFT.

EMBODIMENT 8

FIG. 17 is a view showing the constitution of another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 15. In FIG. 17, a region where a thin filmtransistor TFT is formed and portions of the liquid crystal displaydevice in the vicinity of the region are shown.

The constitution which renders this embodiment different from theembodiment shown in FIG. 15 is that the constitution of the thin filmtransistor TFT as explained in conjunction with the embodiment 7 isadopted to a thin film transistor TFT of a so-called lateral electricfield liquid crystal display device.

Here, in the lateral electric field liquid crystal display device,counter electrodes CT are formed on a liquid crystal side surface of atransparent substrate SUB1 together with the pixel electrode PX andthese electrodes are formed in a comb-shaped pattern in which they meshwith each other.

In the liquid crystal display device having such a constitution, theliquid crystal is driven by a horizontal component of an electric fieldgenerated between the pixel electrodes PX and the counter electrodes CTso that so-called wide-viewing angle characteristics which can provide afavorable image quality even when viewed in an oblique direction areobtained.

With respect to the connection of a source electrode SD2 of the thinfilm transistor TFT with the pixel electrode PX, the condition iscompletely equal to the conditions of the embodiments which have beenexplained heretofore and hence, the connection which has been explainedin conjunction with the previous embodiments can be directly applicableto this embodiment.

EMBODIMENT 9

FIG. 18 is a view showing the construction of another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 15.

Here, the constitution which renders this embodiment different from theembodiment shown in FIG. 15 lies in the constitution of a capacitiveelement Cadd.

That is, a portion of a gate signal line GL arranged in a region wherethe capacitive element Cadd is formed is extended toward a pixel regionside so as to form a projection portion PROL and a distal end portion ofthe projection portion PROL is formed such that the distal end portionis superposed on the pixel electrode PX.

With respect to the thin film transistor TFT, as mentioned previously,the width of the source electrode SD2 is made relatively narrow so thatthe thin film transistor TFT can not ensure the gate-source capacitance(Cgs). In view of the above, this embodiment is configured to ensure thegate-source capacitance in the region where the capacitive element Caddis formed.

In this case, with respect to capacitive elements Cadd of the respectivepixel regions which use the gate signal line GL in common, by adjustingthe capacitive elements Cadd such that the gate-source capacitance issequentially changed from a small quantity to a large quantity from ascanning-signal supply end to an end opposite to the scanning-signalsupply end, a drawback caused by a so-called signal jumping derived fromthe strain of the scanning signal can be prevented and, at the sametime, the adjustment can be performed extremely easily. This is becausethat when the liquid crystal display device includes the thin filmtransistors TFT having the source electrode SD2 of a narrow width, it isdifficult to adjust the gate-source capacitance of the thin filmtransistors TFT.

FIG. 20 is a plan view of a portion of the pixel in this embodimentwhich is prepared by considering dimensions determined at an actualdesign stage based on the constitution shown in FIG. 18. That is, FIG.20 shows the thin film transistor TFT, the capacitive element CAD andportions in the vicinity of these elements.

EMBODIMENT 10

FIG. 19 is a view showing the constitution of another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 15.

The constitution which renders this embodiment different from theembodiment shown in FIG. 15 lies, first of all, in that a protectivefilm PSV is constituted of either the organic material layer alone or asequential laminated body made of an inorganic material layer and anorganic material layer.

Further, in a region where a thin film transistor TFT is formed, aportion of a gate signal line GL is extended along the longitudinaldirection of a source electrode SD2 of the thin film transistor TFT thusforming a projection portion PRO2 and the projection portion PRO2 issuperposed on the source electrode SD2.

That is, in view of the fact that the gate-source capacitance of theprotective film is not sufficiently ensured, a region where the sourceelectrode SD2 of the thin film transistor TFT and the gate signal lineGL are superposed is increased.

Further, the adjustment of gate source capacitance of thin filmtransistors TFT in respective pixel regions which use the gate signalline GL in common is performed by adjusting the length of the extensionportion of the gate signal line GL in the extension direction.

It is needless to say that the constitution of the thin film transistorTFT explained in conjunction with this embodiment is also applicable tothe previously-mentioned lateral electric field liquid crystal displaydevice. Further, the constitution of the thin film transistor TFT ofthis embodiment is also applicable to a liquid crystal display devicehaving other constitution. Still further, the constitution of the thinfilm transistor TFT shown in this embodiment is also applicable to adisplay device using EL (Electro Luminescence) which is provided withthin film transistors TFT.

As has been explicitly explained heretofore, according to the liquidcrystal display device of the present invention, a drawback caused bythe displacement due to misalignment of the thin film transistor or thecapacitive element can be resolved.

1. A liquid crystal display device comprising: a pair of substratesfacing each other in an opposed manner while sandwiching liquid crystaltherebetween; a plurality of gate signal lines arranged in parallel anda plurality of drain signal lines arranged in parallel while crossingthe respective gate signal lines; a plurality of pixel regions eachsurrounded by one of the gate signal lines and one of the drain signallines; a plurality of thin film transistors each driven by a scanningsignal supplied from said one of the gate signal lines; and a pluralityof pixel electrodes to each of which a video signal is supplied fromsaid one of the drain signal lines through a respective thin filmtransistor formed in a pixel region thereof, wherein said respectivethin film transistor includes a drain electrode connected to said one ofthe drain signal lines, a source electrode electrically connected to oneof the pixel electrodes thorough a contact hole and spaced from said oneof the drain signal lines, said source electrode is elongated inparallel with said drain signal line, said one of the gate signal lineshas a first projection portion projecting towards said one of the pixelelectrodes, said first projection portion is elongated in parallel withsaid drain signal line and arranged between said source electrode andanother drain signal line without overlapping therewith in plan view,said another drain signal line is located across said pixel electrodefrom said drain signal line, said first projection portion has a firstoverlapping region overlapping with said one of the pixel electrodes andelectrically insulated from said one of the pixel electrodes, and saidone of the pixel electrodes has a second projection portion projectingtoward a neighboring gate signal line of said one of the gate signallines, said second projection portion has a second overlapping regionoverlapping with the neighboring gate signal line of said one of thegate signal lines, the first overlapping region is separated from thesource electrode without overlapping in plan view, a conductive layer isformed on said one of the gate signal lines, a width of the conductivelayer is wider than a width of said one of the gate signal lines, andthe conductive layer is arranged across both sides of said one of thegate signal lines, a columnar spacer which is arranged to overlap withthe second overlapping region and the conductive laver, the conductivelayer is electrically connected with said one of the pixel electrodesthrough a contact hole, and a width of the columnar spacer is wider thana width of the contact hole.
 2. A liquid crystal display deviceaccording to claim 1, wherein an area of the first overlapping region issmaller than an area of the second overlapping region.
 3. A liquidcrystal display device according to claim 1, wherein a width of thefirst overlapping region is narrower than a width of the secondoverlapping region taken along an identical direction.
 4. A liquidcrystal display device according to claim 1, wherein the conductivelayer overlaps with the first and second projection portions, and thesecond projection portion is on the neighboring gate signal line.
 5. Aliquid crystal, display device according to claim 2, wherein theconductive layer overlaps with the first and second projection portions,and the second projection portion is on the neighboring gate signalline.
 6. A liquid crystal display device according to claim 3, whereinthe conductive layer overlaps with the first and second projectionportions, and the second projection portion is on the neighboring gatesignal line.